1. Field of the Invention
This invention relates to an optical sheet, more particularly to an optical sheet including a light diffusion layer that includes a polymeric resin having bubbles mixed therein.
2. Description of the Related Art
Many approaches have been proposed to increase the range of viewing angles or brightness of a liquid crystal display (LCD). For example, it has been attempted to increase the number of lamps in the light source of the LCD so as to enhance brightness of a display panel of the LCD. However, an increase in the number of lamps will cause a waste of energy and generate a considerable amount of heat. The generated heat will accumulate inside the LCD, thereby deteriorating electronic components in the LCD and shortening the service life of the LCD.
Recently, the brightness of a display panel of the LCD can be enhanced using a brightness enhancement film or a prism film.
The brightness enhancement film traditionally can be manufactured by applying a layer of curable resin, such as acrylic resin, on a polyester substrate, and then patterning the layer of curable resin through imprinting or irradiating with a UV light so as to form microstructures on a surface of the layer of curable resin.
WO 96/23649 discloses an improved method for making a brightness enhancement film. Referring to FIG. 1, the brightness enhancement film 1 obtained from WO 96/23649 includes a substrate 11 and a layer of oligomeric resin 12 formed on the substrate 11. The substrate 11 has a smooth surface 111 opposite to the layer of oligomeric resin 12. The layer of oligomeric resin 12 is formed with a microstructure in the form of prisms 121. Subsequently, the microstructure is subjected to heat treatment so as to reduce deformation thereof.
Although the brightness of the display panel of the LCD can be enhanced using a brightness enhancement film, uneven light beams through the display panel remains a problem. Hence, there is a need in the art to provide a dual-function optical sheet which can enhance the brightness as well as the uniformity of light through the display panel.